There is a need in society to store and distribute hot water. Hot water storage tanks are used to store and distribute (circulate) hot water throughout a plumbing system. Existing hot water storage tanks normally comprise an insulated storage vessel and a heating source. There are many designs for tanks that heat up, store and then deliver hot water to a standard outlet, such as a faucet.
Drainback tanks are types of tanks that are incorporated into systems that employ traditional hot water storage tanks. While adding complexity to these systems, drainback tanks offer a clear advantage to existing systems, as drainback tanks help keep the temperature of the water in hot water storage tanks and systems above freezing, so as to prevent system failure of these hotwater storage tanks. Drainback tanks use convection (a type of heat transfer) to heat the water in a separate hot water storage tank as the water from the hotwater storage tank is passed through a heat exchanger, which receives hot water from the drainback tank. This allows water in storage tanks to be heated when the temperature of the water in the storage tanks decreases, so that the water in the storage tanks does not freeze. Various designs of drainback tanks interacting with hotwater storage tanks are known in the art.
In existing designs, drainback tanks are connected to solar heating loops to heat the water the drainback tanks. Solar heating has become an important technique, as using solar heating allows for a relatively inexpensive way to heat hot water in drainback tanks. Existing designs may use solar heating, however, none of the existing designs provide for an improved design that efficiently uses convection to heat the water in the hotwater storage tank by using a drainback tank, the drainback tank able to achieve increased efficiency of heat transfer between the fluid in the drainback tank and the fluid in the hot water storage tank
Various systems exist that provide for teaching solar heating with drainback tanks. U.S. Pat. No. 5,575,276 (Fossum et al.) discloses a solar thermal water heating system having heat exchangers and a drain back solar water heating tank that is separate from a storage tank. U.S. Pat. No. 4,930,492 (Rich) discloses a solar water heating system and return manifold system employing a floating valve. U.S. Pat. No. 4,574,779 (Hayes) discloses a solar water heating system including a draindown tank located at an elevation lower than that of the heat exchanger.
U.S. Pat. No. 4,562,828 (Koskela) discloses a solar water heating system that includes automatic drainback during freezing conditions. U.S. Pat. No. 4,269,167 (Embree) discloses a closed pressurized solar heating system with automatic valve less solar collector drain-back. Embree discloses a sump tank with internal pipe having a bottom opening at a height well below the operating level of the heat transport fluid within sump tank and also vent hole provide above the initial fluid fill level and above the drained-down thermally expanded fluid level and above the operating fluid level.
However, none of the existing systems provide for a design that has increased efficiency of heat exchange between the fluid of the drainback tank and the fluid of the hot water storage tank. None of these systems provides for a design that allows the hottest water to be fed directly to the heat exchanger, so as to increase the efficiency of heat exchange between the fluid of the drainback tank and the fluid of the hot water storage tank.
It is desirable to provide a system, method and apparatus that achieve optimal or near optimal efficiency in heat transfer between the fluid of the drainback tank and the fluid of the hot water storage tank. It is further desirable to provide a system that quickly allows for heat to be transferred. It is further desirable for a system that transfers the hottest water from the solar heating circuit to the heat exchanger, such that efficient heat transfer occurs.
It is desirable to accomplish these objectives and to provide an improved system that is efficient and provides for efficient heat transfer. Using systems with inefficient heat transfer causes the overall system performance to suffer. Moreover, systems with inefficient heat transfer take longer for the water in the hot water storage to tank to increase in temperature, which is undesired.